1. Field of the Invention
The invention generally relates to mobile communication technologies, and more particularly, to random access procedures applied in machine type communication data for use in mobile communication devices and related data transmission methods.
2. Description of the Related Art
In a typical mobile communications environment, a user equipment (UE) may communicate voice and/or data signals with one or more service networks via cellular stations (or referred to as evolved Node-Bs (eNBs)) of service networks. The wireless communications between the UE and the service networks may be in compliance with various wireless technologies, such as the Global System for Mobile communications (GSM) technology, General Packet Radio Service (GPRS) technology, Enhanced Data rates for Global Evolution (EDGE) technology, Wideband Code Division Multiple Access (WCDMA) technology, Code Division Multiple Access 2000 (CDMA 2000) technology, Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) technology, Worldwide Interoperability for Microwave Access (WiMAX) technology, Long Term Evolution (LTE) technology, and others.
In LTE wireless communication system, a UE may initiate a random access procedure to establish contact with the cellular station (eNB) for any of the following events: (1) Initial access from a RRC_IDLE state; (2) Initial access after a radio link failure; (3) Handover requiring random access procedure; (4) Downlink (DL) data arrival during a RRC_CONNECTED state requiring random access procedure; (5) Uplink data arrival during RRC_CONNECTED requiring random access procedure. Moreover, the random access procedure can be performed by contention-based or non-contention-based manner depending on whether a Random Access Channel (RACH) resource used by the UE is assigned by the network or randomly selected by the UE itself.
Please refer to FIG. 1. FIG. 1 is a message sequence chart illustrating a conventional contention-based random access procedure performed for access to a LTE network by a UE. As shown in FIG. 1, the contention-based random access procedure mainly includes the following four steps: (1) random access preamble step on Physical Random Access Channel (PRACH) (step S110); (2) random access response step on Physical Downlink Shared CHannel (PDSCH) (step S120); (3) scheduled transmission step on Physical Uplink Shared CHannel (PUSCH) (step S130); and (4) contention resolution step on Physical Downlink Control Channel (PDCCH) (step S140). First, when receiving a request, in step S110, a random access procedure is triggered by the radio resource control (RRC) layer or the medium access control (MAC) layer and the UE transmits a RANDOM ACCESS PREAMBLE message to the cellular station by using a randomly selected Random Access CHannel (RACH) resource. Thereafter, in step S120, the cellular station replies a RANDOM ACCESS RESPONSE message including the identification information of the cellular station (e.g. the Cell Global Identity (CGI) of the cellular station) and resource configuration information to the UE, wherein the CGI is used for identifying a node within a network and the resource configuration information is used for indicating the resource configuration required to be allocated for subsequent data transmission. After receiving the valid RANDOM ACCESS RESPONSE message from the cellular station, in step S130, the UE allocates the resources according to the resource configuration information and transmits a SCHEDULED TRANSMISSION message with UE identification information to the cellular station using the allocated resources such that the cellular station may identify the UE. Then, in step S140, the cellular station transmits a CONTENTION RESOLUTION message containing specific UE identity information to the UE such that the contention can be resolved. When receiving the CONTENTION RESOLUTION message from the cellular station, the UE that the specific UE identity information corresponds to can complete the aforementioned random procedure. Detailed operation of the random access procedure is referable in related MAC specification, and is omitted herein for brevity. After the aforementioned random access procedure has been completed, the users can later perform data transmission (step S150).
Moreover, in current LTE wireless communication system, in addition to normal human-to-human (H2H) communications, machine type communication (MTC) is further provided. MTC is a Machine-to-Machine communication, also referred to as the Internet of Things (IOT), which concept is to connect real world objects to the Internet via the embedded short range mobile transceiver using the radio-frequency identification (RFID) for automatic recognition and information interconnecting and sharing for all of the objects.
Similarly, the aforementioned random access procedure has to be performed to enable the data transmission of MTC data regardless the data size of the MTC data to be transmitted each time a MTC is to be performed. In addition, in current LTE specification, it is impossible to transmit small size data over RACH channel as the RACH channel in LTE does not carry any data. Moreover, when a large amount of MTC devices are arranged within a specific area, a large amount of MTC control signaling may be generated, resulting in overloading of Mobility Management Entity (MME), unpredictable transmission delaying and even disabling the service of the network. Therefore, it is a desire to provide a solution to grantee that the loading of the network will not be affected by such MTC application.